Refactor build_github for unknown output dirs.

We can't easily predict what the output directory will be for a Github
release archive.  Get fetch_unpack to tell us.  Add some tests that
won't fail, but at least show us the output.

common_utils.sh

@@ -157,6 +157,8 @@ function fetch_unpack {
     #    url - URL from which to fetch archive
     #    archive_fname (optional) archive name
     #
+    # Echos unpacked directory and file names.
+    #
     # If `archive_fname` not specified then use basename from `url`
     # If `archive_fname` already present at download location, use that instead.
     local url=$1
@@ -170,10 +172,14 @@ function fetch_unpack {
     if [ ! -f "$out_archive" ]; then
         curl -L $url > $out_archive
     fi
-    # Unpack archive, refreshing contents
+    # Unpack archive, refreshing contents, echoing dir and file
+    # names.
     rm_mkdir arch_tmp
     install_rsync
-    (cd arch_tmp && untar ../$out_archive && rsync --delete -ah * ..)
+    (cd arch_tmp && \
+        untar ../$out_archive && \
+        ls -1d * &&
+        rsync --delete -ah * ..)
 }
 
 function clean_code {

library_builders.sh

@@ -77,12 +77,11 @@ function build_github {
     local tag_name=$2
     local configure_args=${@:3}
     local name=`basename "$path"`
-    local name_tag_name="${name}-${tag_name}"
     if [ -e "${name}-stamp" ]; then
         return
     fi
-    fetch_unpack "https://github.com/${path}/archive/${tag_name}.tar.gz"
-    (cd $name_tag_name \
+    local out_dir=$(fetch_unpack "https://github.com/${path}/archive/${tag_name}.tar.gz")
+    (cd $out_dir \
         && ./configure --prefix=$BUILD_PREFIX $configure_args \
         && make -j4 \
         && make install)

tests/test_library_builders.sh

@@ -12,10 +12,15 @@ suppress build_libpng
 suppress build_libwebp
 suppress build_szip
 suppress build_swig
-# We need to find a test for build_github
+# We need to find a failable test for build_github
 # It needs a standalone C library with ./configure script.
-# arb (below) requires a couple of other libraries.
-# suppress build_github fredrik-johansson/arb 2.13.0
+# E.g. arb (below) requires a couple of other libraries.
+# Run here just for the output, even though they fail.
+(set +e ;
+    build_github fredrik-johansson/arb 2.13.0 ;
+    build_github glennrp/libpng v1.6.34 ;
+    build_github wbhart/mpir mpir-3.0.0
+    )
 suppress build_flex
 suppress build_openblas
 suppress build_tiff